//QueueTest.java
//enqueue and dequeue strings to/from a queue.
//the queue can be bounded or unbounded in size.

//LinkedList is used as the queue.  
//Its addLast() is the enqueue operation
//  (end of the LinkedList is the tail of the queue).
//Its removeFirst()is the dequeue operation 
//  (front of the LinkedList is the head of the queue).

import java.util.*;     
import javax.swing.*;

public class QueueTest {

    public static void main(String[] args) {
	String input, userCommand, headOfQueue, newTailOfQueue;
	char op;
	int userAnswer;
	int queueMaxSize=-1;  //fakeout compiler
	boolean isQueueBounded;

	LinkedList myQueue = new LinkedList();  //***create empty queue

        userAnswer = JOptionPane.showConfirmDialog(null,
            "Do you want a bounded size queue?",
	    "",
	    JOptionPane.YES_NO_OPTION);
        if (userAnswer == JOptionPane.YES_OPTION) {
	    input = JOptionPane.showInputDialog("Enter (maximum) size of queue");
	    queueMaxSize = Integer.parseInt( input );
	    isQueueBounded = true;  
	}
	else
	    isQueueBounded = false;  

	printQueue( myQueue );  //show queue at every operation

	do {
	    userCommand = JOptionPane.showInputDialog( "Enqueue or Dequeue or Quit" );
	    op =  userCommand.toUpperCase().charAt(0);

	    if (op == 'E') {
		if (isQueueBounded && myQueue.size()==queueMaxSize)  //***
		    System.out.println("  Queue is full!  Can not enqueue.");
		else {
		    newTailOfQueue = JOptionPane.showInputDialog("Enter string to enqueue");
		    myQueue.addLast(newTailOfQueue);   //***** enqueue
		}
	    }
	    else if (op == 'D') {
		if (!myQueue.isEmpty()) {   //***** check queue (LinkedList) is not empty
		    //***** dequeue Obect cast to needed type:
		    headOfQueue = (String) myQueue.removeFirst();  
		    System.out.println("Dequeued: " + headOfQueue);
		}
		else
		    System.out.println("  Queue is empty!  Nothing to dequeue.");
	    }

	    printQueue( myQueue );  //show queue at every operation

	} while (op != 'Q');

	System.exit(0);
    }
    
    static void printQueue( LinkedList q) {
	System.out.print("Queue is: ");
        //don't normally iterate over a queue.  here for illustration purposes.
        Iterator items = q.iterator();
        while (items.hasNext())
            System.out.print(items.next()+"  ");
        System.out.println();
    }
}